A physical quantity sensor such as an acceleration sensor for detecting acceleration on the basis of a capacitance between a fixed electrode and a movable electrode is disclosed in Japanese Unexamined Patent Application Publication No. 2001-153882. The sensor is a capacitance type acceleration sensor, and the sensor is a foreside processing acceleration sensor, which is provided by processing a foreside surface of a substrate.
In the foreside processing acceleration sensor, a distance between movable portions and a substrate is narrow compared with a backside processing acceleration sensor, which is provided by processing a backside surface of the substrate. The movable portions are, for example, the movable electrode, a massive portion and a spring, which are movable in accordance with the acceleration. Therefore, when the excess acceleration is applied to the sensor, or when moisture or electrostatic force affects the sensor, the movable portions may adhere to the substrate in a case where the movable portions approach the substrate.
Therefore, the sensor includes a protrusion disposed on the substrate to prevent the movable portions from adhering to the substrate. However, an additional process for forming the protrusion on the substrate is necessitated. For example, a film deposition process and an etching process are necessitated to form the protrusion. Therefore, a manufacturing cost is increased.